Muscles of the Upper Extremity: Origins, Insertions, and Actions

Muscles of the Upper Extremity

Anterior Upper Extremity Muscles

The anterior muscles of the upper extremity are primarily responsible for movements such as flexion and abduction of the arm and forearm. Understanding their origins, insertions, and actions is essential for comprehending upper limb movement and function.

• Deltoid

  • Origin: Clavicle and acromion process of the scapula

  • Insertion: Diaphysis (shaft) of the humerus

  • Action: Abducts the arm at the shoulder joint

  • Example: Raising the arm sideways away from the body

• Biceps Brachii

  • Origin: Coracoid process of the scapula

  • Insertion: Radial tuberosity of the radius

  • Action: Flexes the elbow and supinates the forearm

  • Example: Lifting a weight in a biceps curl

• Brachialis

  • Origin: Distal anterior surface of the humerus

  • Insertion: Coronoid process of the ulna

  • Action: Flexes the elbow by lifting the ulna

  • Example: Initiating elbow flexion from a fully extended position

• Brachioradialis

  • Origin: Distal lateral humerus

  • Insertion: Styloid process of the radius

  • Action: Flexes the elbow, especially when the forearm is in a mid-pronated position

  • Example: Hammer curl exercise

Posterior Upper Extremity Muscle

The primary muscle of the posterior upper extremity is responsible for extension of the elbow joint.

• Triceps Brachii

  • Origin: Posterior surface of the humerus (long, lateral, and medial heads also originate from the scapula and humerus)

  • Insertion: Olecranon process of the ulna

  • Action: Extends the elbow

  • Example: Straightening the arm during a push-up

Summary Table: Upper Extremity Muscles

Muscle	Origin	Insertion	Action
Deltoid	Clavicle, acromion process	Diaphysis of humerus	Arm abduction
Biceps Brachii	Coracoid process	Radial tuberosity	Elbow flexion, forearm supination
Brachialis	Distal humerus	Coronoid process of ulna	Elbow flexion (lifts ulna)
Brachioradialis	Distal humerus	Styloid process of radius	Elbow flexion (lifts radius)
Triceps Brachii	Posterior humerus	Olecranon process of ulna	Elbow extension

Additional info: The origins and insertions of muscles determine their actions. For example, muscles that cross the anterior side of a joint typically produce flexion, while those crossing the posterior side produce extension. The biceps brachii and brachialis are synergists in elbow flexion, while the triceps brachii is the primary extensor of the elbow.